One way is intent. If a company's internal communications show that they're intentionally making it addictive, or worse they know it causes harm, you have the smoking gun. This of course doesn't catch all the abuse, but at least it makes it much harder to do this down an entire reporting chain. They have to get really good at winking.

One famous case was Apple suing Samsung over patents. Hard to prove until internal comms surfaced showing intent to copy the iPhone.

Companies are onto this, though, and do training with their staff about how to phrase things in emails to make it look better.